With reference to FIGS. 1 to 3, a photovoltaic system converter can convert electromagnetic energy into electrical energy by photoelectric effect in a temperature, is known as a solar cell and has a conversion efficiency, illumination (S), an output voltage (VPV), an output current (IPV), a loading power, a maximum power, an output power (PPV), a floating charge voltage (VF) and a different maximum power point at different illuminations (S).
The temperature is comprises a first temperature (T1) and a second temperature (T2). T1 is 298 Kelvin (K). T2 is 338 K. The conversion efficiency is 6% to 30%. The illumination (S) has a unit that is abbreviated as W/m2. The output voltage (VPV) is represented by a graph of voltage and current (V-I) with the output current (IPV) for different illuminations. The maximum power point is represented by four black points in FIG. 3 and is affected by illumination (S) and temperature. The floating charge voltage divides the graph of voltage and current (V-I) into a current source zone and a voltage source zone.
The voltage zone is a general operational zone of the solar cell and makes the solar cell stable.
If the loading power increases, IPV increases at the same illumination. When the loading power is greater than the maximum power, VPV will decrease suddenly and make the solar cell operate in the current source zone.
Conduction current mode divides a continuous conduction mode (CCM) and a discontinuous conduction mode (DCM) by directing an inductance current. The continuous conduction mode is when minimal inductance current is greater than 0 amperes. The discontinuous conduction mode is when minimal inductance current equal to 0 amperes.
A maximum power point tracker (MPPT) is a logic circuit for keeping the solar cell from operating at a maximum power point, so a state of a solar cell can be observed and PPV can be adjusted near maximum power.
U.S. Pat. No. 5,327,071 discloses a method and an apparatus for efficiently controlling the power output of a solar cell array string or multiple solar cell array strings to achieve a maximum output power from the strings under varying conditions of use. Maximum power output from a solar array string is achieved through control of a pulse width modulated DC/DC buck converter that transfers power from a solar array to a load or battery bus. The input voltage from the solar array to the converter is controlled by a pulse width modulation duty cycle that in turn is controlled by a differential signal comparing the array voltage with a control voltage from a controller. By periodically adjusting the control voltage up or down by a small amount and comparing the power on the load or bus with that generated at different voltage values causes a maximum power output voltage to be obtained. The apparatus is totally modular and additional solar array strings may be added to the apparatus simply be adding converter boards to the apparatus and changing some constants in the controller's control routines.
However, the foregoing maximum power point tracker is designed by a digital circuit that needs an analog to digital converter, a digital to analog converter and Hall device, decreases efficiency and makes the loading power greater than the maximum power.
Accordingly, a new photovoltaic converter needs to have an analog maximum power point tracker designed with a maximum power limiter.